The present invention relates to latch assemblies, in particular latch assemblies for use with car doors, such as driver's doors, front passenger doors, rear passenger doors. Latch assemblies can be used on any other type of vehicle such as lorries, vans, pickups etc.
Latch assemblies are known to releasably secure doors in a closed position. Operation of an inside door handle or an outside door handle releases the latch allowing the door to open. Subsequent closure of the door will automatically relatch the latch.
Conventional latches (typically mounted on a vehicle door) have a latch bolt, typically in the form of a rotating claw which can be held in a closed position thereby retaining a striker (typically mounted on a door aperture) so as to hold an associated door closed. The latch can also be held in a first safety position by engagement between the pawl and claw. This first safety position is not a fully closed position, rather the door is slightly open, or ajar, but nevertheless held in this ajar position by the latch, i.e. in spite of being in the ajar position, the door will not open.
Traditionally, the claw will have a closed abutment and a first safety abutment. When the pawl engages the closed abutment the door is in the fully closed position and when the pawl engages the first safety abutment the door is in the first safety position. Alternatively the pawl can be provided with two abutments, namely a closed abutment and a first safety abutment. Engagement between the closed abutment of the pawl and the claw will hold the door in the closed position and engagement between the first safety abutment of the pawl and the claw will hold the door in the first safety position.
The pawl is rotatable about a pawl axis into and out of engagement with the claw. Typically the axis about which the pawl rotates is a fixed axis.
The first safety position is provided as a safety measure. With the door fully closed and the vehicle is being driven, in the event that the pawl abutment is disengaged from the claw abutment, the door will open but only as far as the first safety position. The driver and/or other vehicle occupant will be alerted to the fact that the door is ajar and will take appropriate action. In particular, should the pawl become disengaged from the claw in the closed position, the door will not fly open and endanger vehicle occupants.
Car doors have “weather” seals typically around their periphery. These seals are made from elastomeric material and when the door is in the closed and in the first safety position the weather seals are compressed therefore ensuring rain and dirt does not enter the vehicle. As will be appreciated, with the weather seals in a compressed condition, they tend to force the door open and this force is resisted by the pawl and claw.
Under normal conditions when the latch is initially opened the weather seals will push the door open sufficiently far to disengage the striker from the claw. Thus, for a door hinged at its front edge with a latch on its rear edge and a striker mounted on the door aperture, the weather seals might spring the door open at its rear edge by 50 to 100 mm. Clearly, for a driver to enter the vehicle he or she must then fully open the door.
However, under certain circumstances the door seals will not push the door to a position where the striker is fully disengaged from the claw. Thus, consider the circumstances of a vehicle being parked in the evening following a rainstorm. The vehicle and parts of the weather seals will be wet from the rain. Over night the temperature drops, and in this example drops to below freezing whereupon the water around the weather seals freezes and also the weather seals themselves cool to below freezing. The following morning when the driver comes to open the door the weather seals will be adhered to the door by ice and frost. The driver will attempt to open the driver's door but the ice and frost will prevent this. Under certain circumstances the door may move slightly, for example the latch may move 1 mm in an opening direction relative to the striker. The door may then be left in this position and the driver may then attempt and succeed at entering the vehicle via another door. However, as far as the driver's door is concerned, because of the slight movement of the latch relative to the striker, the pawl will not be able to reengage with the closed abutment on the claw (in this example it is the claw that has a closed abutment and a first safety abutment). As the vehicle is driven, it will warm up and the ice and frost will melt. As this occurs, the weather seals will then push the door open, but only as far as the first safety position since the pawl will engage the first safety abutment on the claw and prevent further opening of the door. Thus, under these circumstances it is safe to operate a conventional latch.
Alternative latches also have rotatable pawls but the axis about which the pawl rotates is able to move. Such latches must be able to operate safely even when the door seals are frozen.
Thus, an object of the present invention is to provide an improved door latch.